1 Technical Field
The present invention relates to rotating electric machines that are used in, for example, motor vehicles as electric motors and electric generators.
2 Description of Related Art
There is known, for example from Japanese Patent No. 3633494, an automotive alternator which includes a stator coil that is formed by connecting a plurality of electric conductor segments so as to include a pair of Δ-Y connections; each of the Δ-Y connections is a combination of a Δ-connected three-phase winding and a Y-connected three-phase winding. The alternator also includes a hollow cylindrical stator core which has a plurality of slots that are formed in a radially inner surface of the stator core so as to be equally spaced from one another in the circumferential direction of the stator core. Further, each of the Δ-connected and Y-connected three-phase windings includes a plurality of in-slot portions each of which is received in a corresponding one of the slots of the stator core. Furthermore, the number of the in-slot portions of the Δ-connected three-phase winding and the number of the in-slot portions of the Y-connected three-phase winding in the same slot of the stator core are equal (more specifically, both the numbers are equal to 2). That is, the ratio of number of turns between the Δ-connected and Y-connected three-phase windings is equal to 1:1.
However, with the above configuration, when both the number of turns of the Δ-connected three-phase winding and the number of turns of the Y-connected three-phase winding are equal to N/2, the number of turns of an equivalent Y connection that is equivalent to (or converted from) the Δ-Y connection is only limited to (½+√{square root over (3)}/6)N. For example, with N being equal to 4, the number of turns of the equivalent Y connection is only limited to approximately 3.15.
Moreover, to increase the output of the alternator in a high-speed operating region and improve the efficiency of the alternator, it is necessary to reduce the total number of turns of the stator coil. Further, the total number of turns of the stator coil may be reduced by, for example, the following methods: (1) reducing the number of the in-slot portions of the stator coil in each of the slots of the stator core; (2) employing only Δ connections to replace the Δ-Y connections; and (3) dividing each of the Δ-Y connections into a plurality of Δ-Y sub-connections that are connected in parallel with each other. In contrast, to increase the output of the alternator in a low-speed operating region, it is necessary to increase the total number of turns of the stator coil. Further, the total number of turns of the stator coil may be increased by, for example, the following methods: (4) increasing the number of the in-slot portions of the stator coil in each of the slots of the stator core; and (5) employing only Y connections to replace the Δ-Y connections.
However, the above methods involve the following problems.
In the case of changing the number of the in-slot portions of the stator coil in each of the slots of the stator core (i.e., using the method (1) or the method (4)), it is necessary to change at least one of the dimensions of the stator core and the in-slot portions of the stator coil. That is, it is necessary to change the design of at least one of the stator core and the stator coil.
Consequently, the number of part types will be increased, thereby increasing the manufacturing cost.
In the case of employing only Δ connections to replace the Δ-Y connections (i.e., using the method (2)) without changing the number of the in-slot portions of the stator coil in each of the slots of the stator core, the number of turns of an equivalent Y connection that is equivalent to each of the Δ connections is only limited to (1/√{square root over (3)}) N. On the other hand, in the case of employing only Y connections to replace the Δ-Y connections (i.e., using the method (5)) without changing the number of the in-slot portions of the stator coil in each of the slots of the stator core, the number of turns of each of the Y connections is only limited to N. Therefore, in either of these two cases, it is difficult to meet various requirements for outputs of diversified automotive alternators; it is also difficult to increase the degree of freedom in selection of the stator coil specification.
In the case of dividing each of the Δ-Y connections into a plurality of Δ-Y sub-connections that are connected in parallel with each other (i.e., using the method (3)), the number of the in-slot portions of the stator coil to be connected to an electric in power conversion device (e.g., a rectifier or an inverter) will be increased, thus increasing the man-hours required for connecting the in-slot portions of the stator coil to the electric power conversion device. In addition, it is necessary to change the specification of the electric power conversion device, thus increasing the number of part types.